NUEVO LAREDO, Mexico (AFP) – An American man who was reported missing in March has been identified among 183 corpses found in hidden graves in April in northeastern Mexico, a US diplomat said Wednesday.

"For the moment we can't give details of the victim, but we're giving the relatives consular assistance," said Michael Barkin, US consul for the city of Matamoros, across the border from Brownsville, Texas.

The victim was last seen on a passenger bus traveling between the Mexican cities of Ciudad Victoria and Matamoros in Tamaulipas state, Barkin said.

Another US citizen was missing after traveling on a passenger bus in Tamaulipas, according to the consulate.

The Zetas drug gang, which is fighting a brutal turf war with its former bosses the Gulf cartel in the region, is blamed for the killings in the San Fernando municipality.

Many of the victims were thought to have been pulled off buses traveling to the US border.

The Mexican government has detained 74 suspects in the killings, including 17 police officers who allegedly aided the Zetas.

Authorities also accused the Zetas in the massacre of 72 migrants from Central and South America whose bodies were found piled up at a ranch in San Fernando last August.